Cowgirlheart's Journal, 22 January 2010

well, consider that there are 3500 cal in one pure pound of fat. Your caloric deficit needs to be about 500 cals a day to lose 1 lb a week. Remember, that starvation diets may help you lose weight in the short run. In the long run, however, you'll tend to put on weight. The reason? Your body will prefer to break down muscle tissue over fat tissue when not getting enough calories for its daily activities. So make sure to eat enough for you daily metabolic rate, + or - 1200 cals (how many calories it takes for you to think, breathe, have a heart beat, digest, etc) and to weight train in order to create more muscle. Muscle burns fat and that's really what you want to be doing. Aerobics are important too for a healthy heart. One more thing; don't be discouraged if on the first week or two you put on a little bit of weight while weight training -- muscle weighs twice as much as fat, but is leaner (has a smaller volume), This is a good thing, because with more muscle to burn fat, you'll start losing weight and fat more efficiently after the initial setback. So yes, you probably are gaining muscle mass, this is exciting news!! 

Your clothes don't lie:) If they're fitting better, then you are probably gaining muscle! Which is awesome because, like tribute explained so well, muscle really improves efficiency of weight loss.